T-Pain Is On A Boat: Re: [Electric Boats] LiFe battery

"I am amazed at the money my diesel engine has cost me and the amount of grief it has given me and my wallet (well credit card actually)

It must have esp as every time I think about replacing it with electric it plays up and sucks up the little I had started putting away to go toward replacing it."

Nick:

You hit the nail on the head. I remember back in the diesel days my end of season oil change and winterizing was approaching $100 and that was just routine maintenance and I was doing the work myself. After the head gasket leaked and sprayed water on a cylinder cracking it I spent almost another "boat buck" ($1000) trying to find out why the engine would not start. First by me scratching my head and then paying a mechanic $75 an hour to scratch his head. I'm glad those days are over.

Capt. Mike

http://biankablog.blogspot.com

--- On Tue, 4/19/11, Nicholas Luker <nickluker@gmail.com> wrote:

From: Nicholas Luker <nickluker@gmail.com>
Subject: Re: [Electric Boats] LiFe battery
To: electricboats@yahoogroups.com
Date: Tuesday, April 19, 2011, 12:39 AM

Well according to Jack rickards testing you can punish these cells pretty heavily and he thinks the manufacturers claims are very conservative

But he does stress 2 points heavily

Dont overcharge them

Dont over discharge them

but he does test one down to 1.6 volts at 400 amp load

It does kill it but its nice to now that if it was an emergency like running for shelter with a cyclone up your back side that these cells will give there all

But you would be replacing them the next day!

So it would be an extreme event to do this

driving the cell down to 1.6 volts by pulling 400 amps out of it meets my definition of extreme

surely though 5000 cycles would ,for most people be more than they could do in a lifetime of leisure boating

So a battery pack would be a once off purchase that should last the life of the owner

This is a much better deal than a diesel engine

I am amazed at the money my diesel engine has cost me and the amount of grief it has given me and my wallet (well credit card actually)

It must have esp as every time I think about replacing it with electric it plays up and sucks up the little I had started putting away to go toward replacing it

Nick

On Wed, Apr 6, 2011 at 6:04 PM, Eric <ewdysar@yahoo.com> wrote:

John,

What you're suggesting is kind of like driving your car way past empty on the gauge, until there is less than a cup of gas in the tank before you think about looking for a gas station.

You can interpret the graphs any way you like. However, the spec sheet clearly states that the batteries should deliver greater than 3000 cycles at 0.5C if kept above 80% DoD, and 5000 cycles if kept above 70% DoD.

I take most manufacturer claims with a grain of salt, the specs also show that the cells can take an impulse load of 20C (1800A for the 90Ah cells) without damage. That seems a bit optimistic to me, but might be true. Personally, I try to look at these specs conservatively. I'm setting my expectations to getting only 1500 cycles for my pack if kept above 80%, though they will probably die of old age long before then.

You do need to be careful with lithium though. A single event of discharging a cell to less than 2.5V can ruin it completely. The difference between 2.8V and 2.5V is less than 2% of the rating or less than 1.8Ah for these cells. That can happen pretty fast in real life.

BTW, The batteries that I suggested significantly exceed the performance of your original battery at the weight that you wanted. I'm surprised that you're willing to risk this kind of investement for such a small percentage more range. If you want more range, buy bigger cells like 160Ah that would still be lighter than your original set up. But like I said before, if you buy them, you can treat them any way you like.

Fair winds,
Eric
Marina del Rey, CA

--- In electricboats@yahoogroups.com, "john_casperson" <john_casperson@...> wrote:
>

> Eric--
>
> When I looked at the discharge curve in the link provided below, the LFP battery doesn't fall to the recommended cutoff voltage of 2.8V at a discharge rate of less than 1C until more than 100% capacity is reached.
>
> Since I would be operating at 30 amps (0.33C for the 90AH battery), shouldn't I be able to discharge beyond 80% without damaging the battery, provided I stop prior to reaching 2.8V?
>
> John Casperson
>
> --- In electricboats@yahoogroups.com, "Eric" <ewdysar@> wrote:
> >
> > Here's a quick comparison that I recently wrote: "As a practical comparison, the 160Ah 48V lithium battery bank in my recently converted 1964 Cheoy Lee Bermuda 30 ketch is 60% lighter, 50% smaller and cost 50% more than an high quality 200Ah 48V AGM battery bank that would deliver a similar range under normal 4-5kt operation."
> >
> > So here's what I would do if I was aiming for the performance equivalent of your battery. I have no idea what the Ah capacity of your battery is, so I'll have to focus on the weight.
> >
> > Thundersky 90Ah LiFeYPO4 3.2V cells weigh 7.05 pounds, so 4 cells with strapping would be right around 30 pounds. The cells cost $112.50 a piece for a total cost of $450 dollars. Her's a vendor that sells them. http://currentevtech.com/Lithium-Batteries/Thundersky/Thundersky-90ah-cell-p23.html
> >